One or two subs

Two. I have three and there is bass without excessive boom. Everything blends better with multiple subs.

I use two REL Strata II subs ... more even bass response to be sure, but I can't overstate how much more effort and fiddling it took me to get two subs sounding 'right' vs. just dialing in a single sub. In my room, the secret ended up being to have one of them out-of-phase, and the other one in-phase (and it had to be the correct one, not either/or). That helped me finally narrow in on the elusive 'sweet spot', but it really took me a lot of trial-and-error effort to get there.

With two subs, neither one of them barely breaks a sweat, and you don't even know they're on until you turn them off (if that makes sense :-) and the whole 'rightness' of what you've achieved collapses.

And this probably goes without saying, but definitely run those RELs via the high-level (Neutrik) connections (i.e. off your amp's speaker outputs). Just my $.02.

Thank you all for your responses. After doing some online research, looks like I'll need to go with a one sub set up as my living room is not optimal for a 2 sub set up. If I am facing the tv, the wall is to my left and the additonal space and kitchen is to my right. The subs would go in the left front corner and left rear corner, as I've found online, thats not a good dual sub set up. Any thoughts?

WITHOUT any doubt...2 subs are better than 1. I believe it is best to have 2 of the same subs which ever you choose. Get the best subs you can afford. I use a single Rel in my 2 channel - using the Neutrik Connection. But it is barely on...the crossover is set at 25 htz and the volume is almost off. It just ever so slightly underpins my mains.
BUT<<< in the Theater I use 2 subs...(won't mention the brand)....In theater the subs play a bigger roll. They will probably be crossed over around 80 Htz and be considerable louder. Here's what I find...Having 2 subs eliminates any localization of the low frequencies as well as improving upon room modes - Much smoother response. The bass comes at you like a wave. Ever once in a while, only 1 sub will kick on and the room seems lopsided. then the other kicks on and it's like both feet planted on the ground.
Not to be a party pooper but the rel will run out of gas on some content dished out in Movies - Try the wooshe finger hold at the end of Kung Fu Panda 1- that is a great torture test...Good Luck and happy listening

For the members who have two subs, how is it positioned?